The proposal deals with the interrelationship between peripheral chemosensory mechanisms and the activity of the sympathetic nervous system. The specific objectives are to understand how and to what extent the activities of the pre- and postganglionic fibers to the superior cervical ganglion are regulated by the activties of the peripheral chemoreceptors, respiratory drives from the central nervous system, by the local effects of PO2 and PCO2 on the sympathetic ganglia and by the endogenous dopaminergic mechanisms. The proposal grew out of our active interest in the peripheral chemoreceptors and respiratory chemoreflexes and of the consideration that the existing knowledge in the area does not answer the quantitative as well as qualitative questions raised. The specific experimental procedure is to quantitate pre- and postganglionic nerve responses to selective experimental interventions in anesthetized or unanesthetized decerebrated and spinalized (at C-1 level) cats. One kind of intervention deals with the reflex response of the cervical sympathetic nerves to the chemosensory input in the presence and absence of rhythmic respiratory discharge. The second series deals with the definition of chemosensory properties of the peripheral sympathetic neurons and ganglia independent of the peripheral chemoreceptors and respiratory drive. The third series examines the hypothesis that the endogenous dopaminergic system plays a critical role in the regulation of the postganglionic nerve activity. Perfused superior cervical ganglia will be used to conduct a part of the study. The proposed experimental study is important because the results (1) will tell us how the sympathetic nerve activity is reflexly regulated by the stimuli related to respiration; (2) will extend the observations on the inherent chemosensory properties of the peripheral sympathetic ganglia and compare with those of carotid and aortic bodies; and (3) will indicate the role of the peripheral dopaminergic system in the responses of the sympathetic ganglia. These results will provide the basis for further study of the cellular mechanisms of chemosensing common to both peripheral chemoreceptors and sympathetic ganglia. The practical health related implications are that the chemosensory and chemoreflex control of sympathetic (and reciprocally parasympathetic) nerve activities is critically relevant to respiratory airway and vascular diseases.